The present invention relates to local area networks, and, in particular, to a local area network for the simultaneous, bi-directional transmission of video bandwidth signals.
Local area networks which can transmit video bandwidth signals are known.
FIGS. 1-3 show some prior art networks. In FIG. 1, there is a hub 10, which includes a central processor and an N.times.N crosspoint switch, with N being the number of user paths 18 (the number of inputs and the number of outputs) to be connected to the hub 10. The N.times.N crosspoint switch in the hub 10 permits all the users 12 on the hub 10 to communicate with each other, but it is limited to N users.
FIG. 2 shows one way in which the arrangement of FIG. 1 can be expanded to include more users. In that arrangement, three users 12 have been removed from each hub 10, and the other user ports have been used to connect to other hubs 10 along the paths 14. In this way, more users can be interconnected, but there is a limit to the number of users that can be connected to this system, because every time a new hub is added, a user has to be subtracted from all the other hubs.
FIG. 3 shows a way in which many hubs 10 can be interconnected by connecting them to a bus 20 along the paths 16. With this arrangement, a user 12A connected to the hub 10A on the left can communicate with a user 12C connected to the hub 10C on the right by transmitting a signal along its respective path 18A to its hub 10A, along the path 16A to the bus 20, where it occupies a channel along the entire bus 20, which can be received by a user 12C by passing along the path 16C to the hub 10C and then to the user 12C. This arrangement is limited in that, once all the channels on the bus 20 are used up, no additional signals can be transmitted from hub to hub. If a video conference is being conducted between a user 12A and a user 12C on channel 1, then users 12F and 12G (off the page to the right) cannot conduct another video conference on channel 1 at the same time.
The arrangement of FIG. 3 is also severely limited in the number of connecting lines 16 between each hub 10 and the bus 20, so that, if there is only one connecting line 16A between the hub 10A and the bus 20, then only one channel of the bus 20 can be used by the users 12A at any one time. This means that, if a user 12A is conducting a video conference with a user 12C on channel 1, then another user 12A cannot watch a video on another channel of the bus 20 at the same time. In order to provide more connecting lines to the bus 20, users 12 would have to be removed from the hub 10, which again limits the function of the network.
Another problem with prior art networks is that, if they use twisted pair wiring, they are very limited in the distance over which they can carry signals before the signal degrades to the point that it is not useful.